Clinical and Experimental Allergy, 1990, Volume 20, pages 151-155

The use of Phadiatop® in mass-screening programmes of inhalant allergies: advantages and limitations p. M. MATRICARDI, R. NISINI, J. G. PIZZOLO and R. D'AMELIO Italian Air Force, Immunology Laboratory. Rome, Italy Summary The validity of Phadiatop® as a tool in the mass screening for inhalant allergies was investigated. Seventy-nine out of 600 recruits (13-2%) were classified as allergic to inhalant allergens (68 oculorhinitis; 11 asthma) on the basis of positive history, confirmed by skin testing and/or RAST for the seven most common aero-allergens in Italy. Another 74 subjects had positive RAST and/or skin tests, yet had never experienced allergic symptoms. Phadiatop was positive in 145/600: in 78 out of 79 allergies and in 67 RAST-positive non-allergies. Correlation between Phadiatop and RAST was statistically significant, though higher for grass pollens (r = 0-85. / ' < 0 0 0 1 ) than for Dermatophagoides pteronys.sitms (r - 0 68. P. D. pteronyssinus (d I). cat epithelium (ei). RAST was performed in 200 subjects: 160 selected on ihe basis of positive history and/or positivity in skin tests, and 40

negative controls. Results are expressed as values from 0 to 4-1-, based on the positivity established using the kit reference serum, as well as in ratio units (RU). Sera with RAST positivity for only one of the allergens examined were assumed to be "monospecific' for that allergen, (even if positivity for other. less frequent airborne allergens in our country could not be excluded, it was deemed highly improbable). Total IgE titers Total IgE titers were determined by immuno-enzymatic assay with Phadezym PRIST (Pharmacia). Sera were tested on difterent days using kits from the same stoek. Values are expressed in IU/ml and the cut-off for positivity was arbitrarily set at 220 IU/ml. Phadiatop Immuno-enzymatic paper-disc multiallergosorbent test Phadiatop EIA (Pharmacia) was performed on each serum sample according to the standard overnight procedure. Briefty. 50/(1 of serum were placed on the cellulose disc containing a balanced mixture of adsorbed inhalant allergens (the exact formulation of Phadiatop has not been disclosed by the producer). After 3 lir incubation. discs were washed and incubated overnight with 50 ^1 of peroxidase-conjugated goat anti-human IgE antiserum. After washing. 200 /J of developing solution were added. Reaction was stopped after 2 hr and results obtained by spectrophotometry at 420 nm. Each serum sample was run in duplicate. A series of four negative controls and four reference sera were run every 50 samples. Positivity or negativity was determined when sample absorbance resulted above or below the reference serum value respectively. For statistical analysis net optical density (OD) was also taken into consideration. Final diagnosis On the basisof positive history, confirmed by skin testing and/or RAST. the diagnosis of inhalant allergy was made. This 'final diagnosis' was then compared to the results obtained with PRIST and Phadiatop, Subjects reporting other types of allergies (food, medication, etc.) were diagnosed on history alone. Standard methods were then used to calculate percentages of sensitivity, specificity. positive predictive value, negative predictive value and efticiency for both PRIST and Phadiatop [14]. Statistical analysis Statistical analysis was performed on data fed into an HP 150 computer and processed with PAMFLA data-processing

Advantages and limitations of Phadiatop®

software {Stigma. Paria, Italy). Regression analysis was used for the relationship between Phadiatop OD and RAST units in monospecific sera, and non-parametric tesls were used (Mann-Whitney andchi-square)in all other analyses. Results

153

Total IgE titers The ability of PRIST to discriminate inhalant allergy from non-allergic subjects is reported in Table 1. PRIST showed a sensitivity of 45-6%. failing to disclose allergy in 43 out of 79 allergic subjects (Table I, left side).

Clinical data

Specific serum IgE

Seventy-nine of the 600 subjects studied (13-2%) were found to be allergic to inhalants on the basis of history confirmed by skin tests and/or RAST (Fig. I); 21 additional subjects reported a clinical history of nonrespiratory symptoms (urticaria, angioedema. etc.) suggestive of hypersensitivity to non-inhalant allergens. The allergens most frequently involved were D. pteronyssinus (49-9'>^,). grass pollen (38-8"/^,) and P. judaica (22-4%). Seventy-four subjects (123%) had a positive skin test and/or RAST for one or more inhalant allergens but never experienced any symptoms of allergy.

Phadiatop. One hundred and forty-five ofthe 600 subjects (242%) had positive results in the Phadiatop assay. Phadiatop identified 78 of the 79 subjects with inhalatil allergy, indicating a test sensitivity of 98-7';^.. However, specificity and positive predictive value of the test were lower (87-1 and 53-7'^. respectively), due to the finding of 67 asymptomatic positive subjects (Table 1. right side). Thirty-one per cent of these 67 subjects had a positive family history of allergy to inhalants. The absolute mean absorbance in the Phadiatop-negative group was 0095; the absolute reference serum absorbance ranged between 0120 and 0137. Comparison between symptomalic and asymptomatic subjects positive to Phadiatop is reported in Table 2. The mean Phadiatop absorbance in the asymptomatic group was lower than Uiut of the allergic group ( F < 0 01). who had higher mean specific IgE levels as detected by RAST ( / ' < 0 05). The two groups had ihe same mean number of positive RAST per serum (Table 2); the group of asymptomatic subjects included 24 cases with high levels of specific IgE (RAST class 3 or 4). Total serum IgE did not influence the Phadiatop result; in fact in all subjects with total serum IgE >220 IU/ml (up to 1005 IU/ml in one case) but with negative RAST. Phadiatop was also negative. Among the 200 subjects selected for RAST testing, 152 showed specific IgE to at least one of the seven allergens tested. Sixty-three of these displayed specificity for only one of the allergens tested (apparently monospecific sera for D. pteronyssinus. Grass pollen. P. ojficinalis. cat epithelium and A. tenuis). Monospecific cases for D. pteronyssinus and grass pollen, grouped for allergen specificity and class of RAST

Table 1. Screening of inhalant allergies in 600 Italian male recruits: comparison between PRIST and Phadiatop PRIST (total IgE) (cut-off= 220 IU/ml)

Phadiatop Positive

Negative

Positive

Negative

36

43

Allergies

78

1

64

457

Non-allergies

67

454

456 87-7 822 366 91 4

Sensitivity (%) Specificity (%) Efficiency (%) Positive predictive value (%) Negative predictive value (%)

98-7 87-1 88-7 53-7 998

Table 2. Phadiatop-positive subjects: comparison between asymptomatic and allergic subjects

Phadiatop absorbance (OD) Highest RU level among seven allergens tested Number of RAST positivities Number of positive skin tests * Mann-Whitney (.•'-test. Values represent means ± s.d.

Asymptomatic (n = 67)

Allergic («=78)

0-523 ±0-446 5-96 + 6-8 2-34+1-7 2-43+1-5

0-925 + 0-450 11 57 ±6-9 2-64+1-7 2-75+1-6

P

The use of Phadiatop in mass-screening programmes of inhalant allergies: advantages and limitations.

The validity of Phadiatop as a tool in the mass screening for inhalant allergies was investigated. Seventy-nine out of 600 recruits (13.2%) were class...
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